Heart sound detector and cardiac cycle data are combined for diagnostic reliability

ABSTRACT

From a heart sound signal input the occurrence of a first occurring heart sound is detected. Thereupon a predetermined heart sound enable window time is established, which for a first detection cycle is set to approximately the diastolic interval for the maximum heart rate to be detected. If a second heart sound occurs within this heart sound enable window time, this second heart sound is detected as a systole heart sound. The first heart sound may be detected as a diastole heart sound. If a second heart sound does not occur within the heart sound enable window time the procedure is repeated with increasing heart sound enable time as long as a second heart sound occurs within an increased heart sound enable window time. Cardiac cycle data provided by diagnostic equipment is gated from discriminated heart sound signals and also ECG signals to provide more meaningful diagnostic analysis.

REFERENCE TO A RELATED APPLICATION

This application is a divisional of application Ser. No. 241,388, filedMar. 6, 1981 now matured into U.S. Pat. No. 4,496,873 issued May 8,1984.

BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates generally to the medical diagnostic fieldand more particularly to a method and apparatus for detecting heartsounds and for generating accurately timed reference signals coincidentwith the first and second heart sounds of a cardiac cycle. The presentinvention further relates to the control of medical diagnostic imagingapparatus based on first and/or second heart sound reference signals.

B. Description of the Prior Art

Various medical diagnostic methods and apparatus of the prior art haveattempted to detect heart sounds and to distinguish between the firstand second heart sounds by amplitude or by gating with the R wave of theECG. Further, the prior art arrangements utilize the timingrelationships between successive heart sounds and the first and secondheart sounds for analysis purposes. Other prior art arrangements haveattempted to synchronize, gate or trigger cardiac imaging apparatus onthe basis of heart sound amplitudes, patient cardiac pulse signals, orelectrocardiogram signals and delay techniques.

For example, U.S. Pat. No. 4,094,308 to Cormier detects heart sounds todevelop an electrical phonocardiogram via an inverse filter networkdenoted as a deconvolution function. A phonocardiogram transducer isplaced in contact with the chest of a patient whereupon acousticalenergy of the heart sounds is converted into electrical energy. Theresultant signal waveform after the deconvolution filter providesimpulse functions for each heart sound with the basic purpose of theapparatus to determine the systolic time intervals such as: (1) thepre-ejection phase or period denoted as the elapsed time from the Q-waveonset (in the electrocardiogram waveform) to the opening of the aorticvalve; or (2) the left ventricular ejection time equal to the length oftime the aortic valve remains open as determined by the time differencebetween the two impulse signals. The apparatus distinguishes theimpulses derived from the heart sounds on the basis of amplitude toestablish timing markers for the measurement of the systolic timeintervals and the accompanying heart rate. The larger amplitude signalis stated to occur during the closing of the aortic valve. Pulse heightdetection of the rectified signals resulting from the process isachieved with hysteretic comparators and with digital level convertersregulating extracted voltages and current pulses to trigger digitallogic networks and microcomputer circuits which selectively activateelectronic counters, timers and dividers to measure the pre-ejectionphase, the left ventricular ejection time, the ratio of these twoquantities, and the heart rate.

U.S. Pat. No. 3,318,303 to Hammacher measures heart sounds by use of acontact microphone and provides outputs distinguishing the first andsecond heart sounds of each heart cycle by generating impulsescoincident with each heart sound. While the first and second heartsounds are distinguished and separately analyzed, the first and secondheart sounds are not differentiated by the timing relationships betweenthe heart sounds in the overall heart cycle but merely by the state of aflip-flop which changes state upon the detection of each heart sound tothereby output two series of pulses, one for each heart sound in eachheart cycle. The purpose of the Hammacher method and apparatus is toaccurately determine heart beat frequency by comparing the periodicrates of each of the pulse trains corresponding to the first and secondheart sounds and comparing the heartbeat frequency rate between the twopulse trains. Hammacher also mentions the detection of the firstheartbeat by combination with the R-wave of the ECG.

U.S. Pat. No. 3,581,735 to Gentner, et al. is directed tophonocardiographic apparatus for measuring fetal heart frequency andutilizes the relationships of detected heart sounds in accordance withthe overall period of the heart rate to detect missed heartbeats toprovide accurate indications of the heart frequency. Specifically, theanalysis utilizes physiological criteria to determine if heart soundshave been missed by comparing the time between successive detected heartsounds and the overall heart cycle to determine if an accurate heartfrequency has been detected. For example, if the second heart sound isnot detected and missed, a low heart rate frequency results and theratio between successive heart sounds and the overall period is analyzedand if this ratio is approximately equal, it is determined that a heartsound has been missed; since at low heart rate frequencies such a ratiois physiologically impossible as the time between the first and secondheart sounds is much less than the time between the second heart soundof the first cycle and the first heart sound of the next cycle for lowfrequency heart rates. However, if a high heart rate frequency isdetected and the ratio is approximately equal, it is determined than anaccurate heart rate freqeuncy has been detected. There is nodistinguishing between the first and second heart sounds as the systolicand diastolic events to differentiate the heart sounds.

U.S. Pat. No. 3,498,292 to Jorgensen, et al. is directed to a heartsound sequence indicator to detect and indicate the first and secondheart sounds and their respective intervals on respective systolic anddiastolic indicators. The determination and distinguishing of the heartsounds is achieved by derivation from the electrocardiogram waveform andappropriate timing circuitry and the arrangement does not directlydetect or discriminate heart sounds.

U.S. Pat. Nos. 3,171,892, 3,954,098 3,921,623, Re. 27,042, 3,878,832 and3,132,208 are directed to various prior art techniques that analyzeheart sounds for various purposes. For example, U.S. Pat. No. 3,171,892utilizes an acoustic pickup device for detection of the fetal heart ratewithin another organism and utilizes pulse duration discriminator meansto distinguish the fetal heart rate pulse waves from that of the motherby the pulse width of the heartbeat rate signals. U.S. Pat. No.3,954,098 to Dick et al is directed to heart display apparatus andtriggering of the display from a delayed ECG signal. U.S. Pat. No.3,921,623 is directed to an acoustical heartbeat measuring circuit foranalyzing specific frequencies occurring in the heartbeat and includes afilter having a predetermined frequency response to output an indicationof a number of output signals. U.S. Pat. No. Re. 27,042 is directed toan examination of the characteristics of heart sounds as detected by amicrophone pickup. An electrocardiogram sequencing network controls thesystolic and diastolic interrogation intervals and thus the heart soundsare detected under control of the electrocardiogram sequencing. U.S.Pat. No. 3,878,832 is directed to a system for analyzing heart defectsas detected by random noise from a composite signal that includes aperiodic portion and a random noise portion. U.S. Pat. No. 3,132,208 isdirected to a variable conductivity gate circuit for amplifierselectivity in an electronic stethoscope.

Considering various prior art techniques for utilizing heart soundsand/or ECG signals to control diagnostic display, U.S. Pat. No.3,220,404 to DelLucchese is directed to a combined X-ray andphonocardiographic camera wherein the horizontal sweep of a displaydevice is gated when heart sounds detected by a microphone exceed apredetermined level.

U.S. Pat. No. 2,190,389 to Strauss, et al. is directed to the control ofX-ray apparatus by means of a heart movement or pulse beat pickup andproviding an adjustable time delay to activate the X-ray tube of theapparatus. A pulse pickup is affected by means of a compression cuff orbag applied to the wrist with pressure variations being transmitted toact upon a piezoelectric crystal.

U.S. Pat. No. 3,825,751 to Geratsdorfer is directed to a method ofactivating X-ray apparatus by means of electrocardiogram signals andproviding a predetermined delay to activate the apparatus forapproximating the appropriate time of activation based on theelectrocardiogram waveform.

U.S. Pat. No. 3,626,932 to Becker is directed to a method and apparatusfor producing a double exposure, X-ray photograph of a heart at twodifferent points during the cardiac cycle by causing an X-ray machine toproduce an X-ray burst at a first given point in a cycle and thenanother burst at a second different point during the cycle. The methodand apparatus utilizes a synchronizer for detecting the R-wave peak fromelectrocardiogram waveform and includes various adjustable pulse delaymeans for proper synchronization.

U.S. Pat. No. 3,557,371 to Becker is similarly directed to a method andapparatus for calibrating a cardiac X-ray synchronizer to cause an X-raymachine to produce an X-ray burst at a given adjustable point in thecardiac cycle of a patient disposed in the burst path. The R-wave peakin the electrocardiogram waveform is detected to produce a signalactuating the machine at a given adjustable time after the R-wave peak.

U.S. Pat. No. 2,152,045 to Gulland is directed to a body operated switchapparatus for synchronizing X-ray exposures utilizing a mercury switchmechanically operated by pulse, respiratory or other movements of thebody and includes delayed action for timing exposures of X-rays or otherphotographs of the heart, lungs, etc.

U.S. Pat. No. 3,344,275 to Marchal, et al. is directed to radiologyapparatus for effecting a simultaneous recording of a relatively slowvariation of density such as of the lungs during respiration and also ofthe small variations of density due to the circulation of the blood.Activation of the two channels of information is controlled by anelectrocardiogram input.

U.S. Pat. No. 4,240,440 to Groch et al. is directed to method andapparatus for obtaining a nuclear kymogram of regional heart wall motionin synchronism with a display of the ECG signal; the dispaly beingtriggered under the control of the ECG signal.

Various other display arrangements controlled by the ECG signals aredescribed in the following publications:

"Clinical Assessment of Left Ventricular Regional Contraction Patternand Ejection Fraction by Height Resolution Gated Scintography", Bermanet al., Journal of Nuclear Medicine, Volume 16, Number 10, pp. 865-874;

"Thallium-201 Myocardial Imaging: Characterization of theECG-Synchronized Imager", Hamilton et al., Journal of Nuclear Medicine,Volume 19, Number 10, pp. 1103-1110;

"Left Ventricular Function in Acute Myocardial Infarction Evaluated byGated Scintiphotograph", Rigo et al., Circulation, Volume 50, pp.678-684, 1974;

"A Real-Time System for Multi-Image Gated Cardiac Studies", Bacharach etal., Journal of Nuclear Medicine, Volume 18, Number 1, pp. 79-84, 1977;and

"Comparison of Defect Detection or Ungated vs. Gated Thallium-201Cardiac Imager", McKusick et al., Journal of Nuclear Medicine, Volume19, Number 6, p. 725.

U.S. Pat. No. 3,993,995 to Kaplan, et al. is directed to a respirationmonitor and utilizes arrangements for the automatic triggering of anX-ray machine at the instance of respiration extremes.

Thus, while the arrangements of the prior art have attempted to detectand distinguish between heart sounds, these prior art arrangements arenot entirely suitable for accurately distinguishing between the firstand second heart sounds and for providing accurately timed referencesignals synchronized with the first and/or second heart sounds. Further,the prior art arrangements do not provide accurate and efficientdiagnostic analysis to synchronize analysis data and/or images byaccurately timed first and/or second heart sounds.

SUMMARY OF THE INVENTION

Accordingly, it is a principal object of the present invention toprovide a method and apparatus for detecting heart sounds and forgenerating accurately timed reference signals coincident with the firstand second heart sounds of a cardiac cycle based on the timerelationship of the detected heart sounds.

It is another object of the present invention to provide a method ofcontrolling diagnostic apparatus to provide accurately synchronized dataanalysis and/or images of cardiac function under the control of accuratefirst and/or second heart sound signals.

It is a further object of the present invention to provide a method andapparatus for providing first and second heart sound signals wherein theheart sound signals are distinguished and provided only when the twosequenced signals satisfy a time relationship such that both signalsoccur within a window of time, the appropriate window of time beingselected in accordance with the cardiac cycle of the patient beingmonitored and predetermined characteristics of the cardiac cycle.

It is yet another object of the present invention to provide a method ofcontrolling cardiac diagnostic apparatus wherein an accuratelydetermined second heart sound signal is utilized to correct the gatingof analysis data or to accurately initiate analysis throughout thediastolic interval starting at systole.

It is a further object of the present invention to provide a method ofcontrolling the accumulation of cardiac data through the use of accuratefirst and/or second heart sound signals for patients with pacemakers,serious arrhythmias and other cardiac characteristics that causedistortion of the electrical impulse denoted as ECG or functionalrelationships that cause spurious heart sounds that could be erroneouslydetected as the first or second heart sound.

Briefly, these and other objects of the present invention areefficienctly achieved by providing a method and apparatus for detectingheart sounds and for generating accurately timed reference signalscoincident with the first and second heart sounds of a cardiac cycle.The detection and generation of the first and second heart sound signalsare based on the time relationship of the detected heart sounds.Further, there is provided a method of utilizing the generated first andsecond heart sound reference signals for synchronization or gating ofmedical diagnostic imaging apparatus. Thus the medical diagnosticimaging apparatus is controlled to accept data or an image as determinedby the first and/or second heart sound reference points for improveddiagnostic purposes. For example, the diagnostic apparatus may becontrolled to provide improved diagnostic information for phase analysisof gated blood pool studies. The heart sound detecting apparatus furtherprovides for detection based on either the timing relationship betweenthe heart sounds or by the R-wave of the ECG signal. The heart sounddetecting apparatus includes a display to selectively provide a read-outof the time interval or rate of various heart cycle parameters includingfirst to second heart sound time interval, first heart sound to firstheart sound rate or time interval, heart rate, heart cycle period,R-wave to R-wave rate or interval, R-wave to first heart sound timeinterval, R-wave to sound heart sound time interval, and R-wave toR-delay signal as selected on the apparatus. The heart sound detectingapparatus includes arrangements for the simultaneous recording andplayback of heart sounds and the ECG waveform signals on a commonchannel or track.

The invention both as to its organization and method of operationtogether with further objects and advantages thereof will best beunderstood by reference to the following specifications taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram representation of heart sound detection andgating apparatus to generate first and second heart sound signals inaccordance with the present invention;

FIG. 2 is a block diagram representation of ECG gating apparatus andrecording apparatus of the present invention for use with the heartsound detection and triggering apparatus of FIG. 1;

FIG. 3 is a graphic representation versus time of the operation of theheart sound detection and triggering apparatus of FIGS. 1 and 2 in atimed mode of operation and a typical heart cycle illustrating the firstand second heart sounds and the ECG waveform associated therewith;

FIGS. 4a through j when assembled as shown in FIG. 4k form a schematic,logic and block diagram representation of a detailed specific embodimentof the heart sound detection and triggering apparatus of FIG. 1.

FIG. 5 is a representation of various timing diagrams and signalrelationships in the specific embodiment of the heart sound detectionand triggering apparatus of FIG. 4 regarding a first to second heartsound timing detection mode of operation;

FIG. 6 is a representation of various timing diagrams and signalrelationships in the specific embodiment of the heart sound detectionand triggering apparatus of FIG. 4 regarding an ECG R-wave detectionmode of operation;

FIG. 7 is a graphical representation useful in illustrating theoperation of the present invention of FIG. 4 and illustrating look-uptable ranges of operation for setting timing windows in connection withheart sound detecting; and

FIG. 8 is a block diagram representation of diagnostic apparatus for usewith the present invention and illustrating the control of diagnosticapparatus in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, the heart sound detection and triggeringapparatus 10 of the present invention includes a heart sound signalselector switch 12 that selectively connects one of three heart soundaudio signal inputs 14, 16 or 18 to a common output 20 of the selectorswitch 12.

The heart sound signal input 14 is derived at the output of a soundtransducing circuit 22 from either a single sound transducer input 24 orform dual sound transducing inputs 26, 28. The second transducing inputs24, 26, 28 are connected in various applications to sound transducingapparatus or microphones placed on the chest of a patient underinvestigation. The dual sound transducing inputs 26 and 28 are eachrespectively connected to a sound transducer placed on a different chestposition. Accordingly, one sound transducer receives a higher amplitudefrom the heart sounds of a patient through the chest cavity while thesecond sound transducer receives a relatively lower amplitude heartsignal based on the positioning of the second sound transducer at asomewhat more remote location from the heart position. Thus, the soundtransducing inputs at 26 and 28 receive essentially equal inputs ofbackground sounds and body sounds as modified by the patient's body forcommon mode rejection of these unwanted background sounds such asrespiration or room noise. The sound transducing inputs 24, 26 and 28are connected to a preamplifier stage 30. The outputs 32 and 34 of thepreamplifier stage 30 are connected to two inputs of a differentialamplifier stage 36. In the case of dual sound transducer inputs,differential amplifier 36 responds only to the differential heart soundsignals and essentially rejects all common mode unwanted signals. In thecase of a single sound transducer at 24, the output 34 is amplified bythe differential amplifier stage 36. The amplified output 38 of thedifferential amplifier stage 36 is processed by a filter stage 40 toprovide the heart sound signal input 14. The filter stage 40 is arrangedto eliminate any frequencies unrelated to first and second heart sounds.

The heart sound signal input 16 is provided by an externalamplifier/filter arrangement referred to generally at 42 for use withexternal sound transducing and amplifying apparatus. The heart soundsignal input 18 is provided at the output of a two Khz. cutoff low passfilter stage 44 from a recorded heart sound input 46. The recorded heartsound input 46 is provided at the output of a recorded heart sound ECGand buffer stage 48 (see FIG. 2). The input to the recorded heart soundECG and buffer stage 48 is connected to a playback transducing output 50of a recorder (FIG. 2). The recorded heart sounds and ECG waveforms of apatient are recorded on a common channel or track by a recordingarrangement for use with the present invention for analysis at a timesubsequent to actual recording of the heart sounds and the ECG waveformof a patient under investigation for future, further analysis.

The output 20 of the heart sound signal selector switch 12 is connectedthrough a filter stage 52. In a specific embodiment the filter stage 52is a low pass filter with a cut-off frequency below 500 Hz. which isarranged to eliminate some of the audio signals associated with heartsound transducing but which are unrelated to the actual first and secondheart sounds. The output 54 of the filter stage 52 is connected throughan AGC amplifier stage 56 to normalize signal levels for the subsequentdetection and gating stages of the arrangement 10.

A first output 58 of the AGC stage 56 is connected through a heart sounddisplay buffer stage 60 to provide a display output 62 of heart soundsfor analysis. A second output 64 of the AGC stage 56 is connected as asumming output for recording along with ECG waveforms to a recordingarrangement as will be discussed in more detail in connection with theECG gating apparatus of FIG. 2.

The output 64 of the AGC stage 56 is also connected through a positiveenveloper and squaring stage 66 which essentially repositions allnegative portions of the heart sound waveform at 64 into the positiveenveloped signal domain and also squares the input to accentuate theheart sound signals in the positive envelope. The output 68 of thepositive enveloper and squaring stage 66 is connected through acomparator or peak detector stage 70 to provide at output 72 a digitaltrigger signal in response to the heart sounds.

Referring now to FIG. 3, typical first and second heart soundsassociated with a typical cardiac cycle are illustrated in conjunctionwith the ECG waveform with the heart sounds defining the systolic anddiastolic intervals of the overall cardiac cycle.

The digital heart sound trigger signals at 72 are connected to adigitally variable digital filter stage 74. The digital filter stage 74provides pulse shaping and a heart sound signal pulse output at 76 inresponse to each heart sound trigger signal at 72 in accordance with adigital selection signal at 78. The digital filter stage 74 inaccordance with the digital selection signal 78 also provides a variablelock-out time window such that the digital filter is inhibited fromoutputting additional heart sound signals at 76 within the time intervalof the lock-out time immediately after a heart sound signal output at76.

The digital selection signal 78 is provided by a digital integrator andtiming control stage 80 that determines appropriate digital selectionsignals at 78 in accordance with the cardiac cycle and heart soundtiming of the apparatus 10. The digital integrator and timing controlstage 80 receives data signals at 82 from a display and control file 84.A data address input 86 is provided to the display and control file froma system timing control stage 88.

The digital heart sound pulse signals at 76 are connected to a windowtrigger selector stage 92 and a window mode control stage 100. Thewindow trigger selector stage 92 provides a digital trigger controlsignal at 94 to control operation of a digitally variable time windowstage 90 in accordance with either the digital heart sound pulse signalat 76 in a timed mode (T-mode) of operation or an ECG R-wave signal 96provided as an input to the window trigger selector stage 92 from theECG apparatus of FIG. 2 in an ECG R-wave (E-mode) of operation.

The trigger selection of the window trigger selector stage 92 isaccomplished by a selection input from a selection switch arrangement at97. In a first E-mode switch state of the arrangement 97, the windowtrigger selector stage 92 provides a trigger control signal at 94 inaccordance with the ECG R-wave signal at 96. In a second T-mode switchstate of the switch arrangement 97, the window trigger selector stage 92provides a trigger control signal at 94 in accordance with the heartsound pulse signal at 76.

The digitally variable time window stage 90 also includes as an inputthe digital selection signal 78. The digitally variable time windowstage 90 sets one or more variable time windows in accordance with thedata state of the digital selection signal 78 and the mode of operationas set by switch 97. In accordance with the variable time window orwindows, the digitally variable time window stage 90 providesappropriately timed heart sound enable signals at 98 and at 104 to thewindow mode control stage 100.

The window mode control stage 100 in accordance with the inputs from theheart sound enable signals 98 and 104, and the digital heart sound pulsesignals at 76 outputs a first heart sound trigger signal at 106 and asecond heart sound trigger signal at 108.

Thus, the digital filter stage 74, the window trigger selector 92, thedigitally variable time window stage 90, and the window mode controlstage 100 function in combination as a digital time filter as variablyset by the digital selection signal 78 to detect the heart sound pulsesignals at 76 and distinguish between the first and second heart sounds.The variable time windows are automatically adjusted by the heart sounddetection and triggering apparatus 10 to accurately distinguish betweenthe first and second heart sounds for patients with heart rates in aspecific predetermined range; e.g., 15-250 beats (heart cycles) perminute in a specific embodiment. The operation of the apparatus 10 toadjust the time window and to detect the heart sounds will be discussedin more detail hereinafter.

The first heart sound trigger signal 106 and the second heart soundtrigger signal 108 are provided as inputs to a system trigger selectoutput stage 110 that functions as a selector switch to output a systemtrigger output signal at 112 for the triggering and control ofdiagnostic equipment. The trigger select stage 110 also includes the ECGR-wave trigger signal 96 and an ECG R-wave delayed trigger signal 116 asinputs. The signals 96 and 116 are provided from the ECG apparatus ofFIG. 2. The system trigger output 112 is also connected through adisplay trigger stage 118 to provide a display study trigger signal 120at the appropriate level.

The first and second heart sound trigger signals 106 and 108respectively and the ECG signals 96 and 116 are also connected as inputsto a display input selection and pulse-to-pulse gate stage 122. Thedisplay selection and pulse gate stage 122 includes a selection switch123 for selecting one of a predetermined number of parameters fordisplay selection as rates (beats per minute) or time intervals (inmilliseconds), including, for example, in a specific embodiment first tosecond heart sounds time interval (F-S), first heart sound to firstheart sound time interval (F-F) or (F-F) rate, ECG R-wave to R-wave rate(R-R rate) or time interval (R-R), ECG R-wave to first heart sound timeinterval (R-F), ECG R-wave to second heart sound time interval (R-S),and ECG R-wave to R-wave delayed time interval (R-RD) as set on a delayselector. A display 130 discussed hereinafter is controlled to displayeach of the parameters. The display selection and pulse gate stage 122responds to the selected trigger signals as set on the selection switch123 and provides appropriate corresponding timing signals, displaysignals and mode select signals to provide accurate time interval orrate data for display purposes and also for system control.

Specifically, the display selection and pulse gate stage 122 provides arate/time interval select output at 124 to appropriately control thesystem timing control stage 88 in a binary mode corresponding to rateand in a decimal mode corresponding to time interval. The rate/timeinterval select output 124 is also connected as a selector input to atime interval or rate selector stage 126.

The time interval or rate selector stage 126 outputs display data at 128to the display 130. The time interval or rate selector stage 126includes time interval data inputs at 86 from the system timing controlstage 88. Further, the time interval or rate selector stage includesrate data inputs at 132. Thus, the time interval or rate selector stage126 outputs at 128 either the rate data from the rate data input 132 orthe time interval data from the time interval data input 86 inaccordance with the selector signal at 124. The system timing controlstage 88 includes a clock input at 134 from a system timing clock 136.The system timing clock 136 is enabled to output clock pulses at 134when enabled by a clock enable input 138 from the display selection andpulse gate stage 122. The system timing control stage 88 also includes apreset input at 140 to preset the stage 88 at the start of a timeinterval or rate determination based on the first trigger signalreceived by the display input and pulse gate stage 122 in accordancewith the selected functions. Further, the display selection and pulsegate stage 122 also stops the time interval or rate determination bymeans of the enable signal 138 to the system timing clock 136.

For example, if the display selection and pulse gate stage 122 is set tothe first to second heart sound display selection mode, the systemtiming control stage 88 will be controlled to start timing intervalcount data upon the occurrence of the first heart sound pulse signal at106 and the system timing control stage 88 will stop the count upon theoccurrence of the second heart signal. The accumulated count at output86 then corresponds to the time interval of first to second heart soundsignals. The time interval or rate select stage 126 in accordance with atime interval select signal at 124 provides the time interval data at128 for display.

Considering a rate display, the display and control file 84 is addressedby the data output 86 with the system timing control functioning tocount in the rate mode as set by the rate/time select signal 124. Inresponse to the address at 86, the display and control file 84 outputsat 132 the rate data corresponding to the count data address input. Withthe select signal 124 in the rate mode, the time interval or rate selectstage 126 outputs the rate data 132 at the display output 128.

Referring now to FIG. 2 and considering the ECG gating apparatus 150,the ECG input leads generally referred to at 152 include a conventionalthree lead ECG input from electrocardiogram apparatus including a humanground and the left shoulder and right side patient sensors. The ECGinputs 152 are connected to an ECG isolation amplifier stage 154 thatprovides a signal at 156 to a DC restorer stage 158. The DC restorerstage 158 is provided to stabilize the DC level of the ECG waveformwhich commonly experiences disturbances of the DC level. The output 160of the DC restorer stage 158 is connected as a first selection input toan ECG selector switch 162. The output 164 of the selector switch 162 isconnected to an AGC amplifier stage 166.

The ECG selector switch 162 also includes a second input 168 from anexternal ECG input arrangement at 170. A third input 172 to the selectorswitch 162 is provided from a recorded ECG signal path. The recorded ECGsignal at 172 is provided at the output of an ECG demodulator stage 174.The ECG demodulator stage 174 receives an input at 46 from the recordedheart sound ECG buffer stage 48 from the recorder input 50. The ECGdemodulator stage 174 demodulates the recorded ECG signal which ismodulated by a 7 Khz. signal (in a specific embodiment) for recordingand includes a high-pass filter having a band pass starting atapproximately 5 Khz for a specific embodiment of 7 KHz. modulationfrequency.

The AGC stage 166 normalizes the selected input at 164 from the selectorswitch 162 to appropriate levels for the remaining gating circuitry ofthe ECG apparatus 150. The output 176 of the AGC stage 166 is connectedto an ECG filter stage 178 which eliminates unwanted frequency signalsassociated with the ECG waveform. The ECG filter stage 178 also providessome degree of isolation for the R-wave of the ECG waveform.

The ECG filter 178 provides an output at 180 connected through an ECGdisplay buffer stage 182. The ECG display buffer stage 182 provides anoutput at 184 for display apparatus to display the ECG waveform.

The output 180 of the filter 178 is also connected through an ECGmodulator stage 186 that modulates the ECG waveform at 180 with a 7 Khz.modulation frequency to provide an ECG modulated waveform for recordingat output 188. The output 188 is connected to an ECG modulated and heartsound summing amplifier driver stage 190 along with the heart soundsignal 64. The summing amplifier and driver stage 190 provides an outputat 192 to recording apparatus to record the combined heart sound and ECGmodulated waveforms on a common channel or track on an appropriaterecording medium such as tape.

The ECG filter stage 178 also provides an output 194 to an ECG absolutevalue amplifier stage 196. The ECG absolute value amplifier stage 196transforms or folds the negative portion of the ECG waveform into thepositive half and provides processing isolation to account for thepossibility of misplaced leads causing false triggers from the ECGwaveform from portions of the ECG waveform other than the R-wave.

The output 198 of the ECG absolute value amplifier stage 196 isconnected through an ECG squaring circuit 200 to provide an output 202to an ECG peak detector stage 204. The ECG squaring circuit 200accentuates the R-wave of the ECG waveform. Thus the ECG peak detectorstage 204 receives a waveform to allow appropriate and accuratetriggering on the R-wave.

The output 206 of the ECG peak detector 204 is provided to an ECGdigital filter stage 208. The ECG digital filter stage 208 provides alock-out of any non-R-wave triggering signals by providing a lock-outtime period on a digital basis for a predetermined period of timefollowing the occurrence of the R-wave. The output 210 of the ECGdigital filter stage 208 is connected through an ECG delayed triggerstage 212 to provide the ECG R-wave delayed signal at 116 connected asan input to the display selection stage 122. The output 210 of the ECGdigital filter stage 208 is also connected through an ECG trigger stage214 to provide the ECG R-wave trigger signal 96.

Considering the operation of the heart sound detection and triggeringapparatus 10 in more detail and referring again now to FIGS. 1 and 3,with the trigger mode selection switch in the time or T-mode, thedistinction between the first and second heart sounds is accomplishedbased solely on the timing relationships between the heart sound signalsat 76. When using the terms first and second heart sounds, reference isbeing made respectively to the end diastole and end systole sounds. Toavoid confusion, the following discussion will use the terms diastoleheart sound and systole heart sound to differentiate from the firstoccurring heart sound and subsequent heart sounds at 76.

When operation of the detection process commences in the T-mode for eachheart cycle, the digital filter stage 74 is set by the digital selectionsignal 78 to provide a lock-out or inhibit window of time equal to theshortest systolic time interval for the file value selected in thedisplay and control file 84.

The apparatus 10 begins the detection process for each heart cyclestarting with file values for the maximum heart rates to be detected.This procedure ensures that the heart sounds will be properly detectedand that no valid heart sounds will be missed due to the inhibit windowin the filter stage 74 being too long. With the filter stage 74 set toprovide an inhibit time of the shortest systolic interval for themaximum heart rate, no valid systole heart sound will be inhibited ormissed if the first pulse at 76 from a heart sound and the second pulseat 76 from a heart sound occur with the shortest systolic interval.

Upon the occurrence of a first pulse at 76, that may correspond toeither diastole (first heart sound) or systole (second heart sound), thedigital filter 74 inhibits signals at 76 due to false or extraneousheart sounds.

In response to the heart sound signal pulse at 76 and the heart soundenable signal at 98, the window mode control stage 100 provides a pulsesignal at the first heart sound trigger output 106.

After the termination of the brief heart sound signal pulse at 76resulting from a first received heart sound (which could be diastole orsystole), the digitally variable time window stage 90 enables the heartsound signal at 98 for a predetermined window of time as variablyselected by the selection signal 78 from the digital integrator andtiming control stage 80 in accordance with the file value addressed at86 and output at 82 from the display and control file 84.

At this time, the file value corresponds to the diastolic interval ofthe maximum heart rate. This window of time characterized by the enabletime of signal 98 is the safe period of time within which to interrogatefor the second heart sound (systole) without erroneously detecting adiastole pulse if the heart rate of the patient being monitored is amaximum. This window of time at 98 also corresponds to a systolicinterval which is substantially greater than the systolic interval forthe maximum heart rate.

If a second heart sound occurs at 76 during the enable time of thewindow enable signal at 98, the window mode control stage 100 provides asecond heart sound trigger pulse signal at 108. Thus, in this example,the second heart sound received corresponds to systole and the firstheart sound received corresponded to diastole.

If no heart pulse signal at 76 occurs during the window enable time ofthe signal 98, either the first heart sound received was systole or theheart rate is substantially lower than the maximum rate first set forinterrogation by the digital integrator and timing control stage 80.

The detection process proceeds with the digital integrator increasingthe enable window time at 98 and the inhibit window time of the digitalfilter 74 in data steps and in a predetermined manner according to thefile table in stage 84. At some point along the descending table, thefirst heart sound detected will be diastole and the second heart sounddetected will be systole and will occur within the enable window time ofthe signal at 98. In accordance with the actual heart rate of thepatient being interrogated, this procedure might encompass several heartcycles.

The file table data in the display and control file of stage 84 isselected to provide a predetermined number of table ranges to cover theentire range of heart rates to be interrogated from the maximum heartrate to the minimum heart rate.

Considering now operation of the heart sound detection and triggeringapparatus 10 in the ECG R-wave triggered mode (E-mode), the occurrenceof the ECG R-wave signal at 96 via the window trigger selectorconditions the digitally variable time window stage 90 to provide afirst heart sound enable time window at 98. The first heart sound enabletime window in the E-mode is a fixed time interval throughout thedetection process. The digital filter 74 after the occurrence of a heartsound at 76 provides a variable inhibit window time in accordance withthe selection signal at 78 as in the T-mode.

Upon the occurrence of a first received heart signal pulse at 76 in theE-mode within the enable time of signal 98, the window mode controlstage 100 outputs a first heart sound trigger signal at 106 in responseto the heart sound pulse at 76 and the first heart sound enable signal98. Further, a second heart sound enable signal at 104 is enabled for avariably programmed window time via signal 78. In a specific embodiment,the second heart sound enable signal at 104 is provided after thetermination of the first heart sound enable signal at 98 rather thanafter the occurrence of the first heart sound pulse at 76 or the firstheart sound signal at 106.

The variable time enable window provided by the signal 104 is set by thedigital integrator 80 and the file table in stage 84 to be equal to theallowable maximum diastolic interval for the file table values beinginterrogated at the time. For example, at the start of the detectionprocess, the maximum heart rate is possible and thus the maximumdiastolic interval corresponds to the diastolic interval for the maximumheart rate.

Upon the occurrence of a heart sound pulse at 76 occurring after thewindow inhibit time of the digital filter 74, the window mode controlstage 100 provides the second heart sound pulse trigger signal at 108 ifthe heart sound signal at 76 occurs within the enable time window set at104. If the heart sound pulse at 76 does not occur within the enabletime at 104, the apparatus 10 proceeds to move through the file table ina predetermined manner until the second heart sound is detected withinthe enable time window at 104 with successively longer enable windowsbeing established as the process continues until proper detectionoccurs.

After proper detection occurs, the apparatus 10 continues to detect thefirst and second heart sounds and provides on the display 130 a read-outof the time interval or rate of the function selected on the displayselection switch 123. If the heart rate of the patient varies during thedetection process after proper detection has occurred, the display andcontrol file stage 84 and the digital integrator stage 80 are addressedin accordance with the previous time interval at 86 to appropriatelyvary the control time windows to maintain proper detection. If properdetection sequence or synchronization is lost due to rapid heart ratechange or false input conditions, the apparatus 10 reestablishes properdetection or synchronization in the same manner in which originaldetection was achieved as discussed hereinbefore.

Referring now to FIG. 4 wherein identical reference characters andnumerals refer to corresponding elements and stages of FIG. 1, aspecific embodiment of the heart sound detection and triggeringapparatus 10 to achieve the objects of the heart sound detection andtriggering apparatus 10 will now be discussed. Considering now thedigital filter stage 74 (FIG. 4g), the digital selection signal 78including the four control leads W1 through W4, is connected to controlthe respective stages of a four stage analog switch 250. The analogswitch stages of 250 in accordance with the selection signal 78selectively connect one or more resistors in the resistor array 252 froma reference supply to the timing input of a monostable stage 254. Thetime period of the monostable is thus selected in accordance with theselection signal 78 by one or more of the resistors in the array 252being connected in parallel to the timing input. The heart sound signalat 72 from the comparator stage 70 is connected to trigger a monostablestage 256. the Q output of the stage 256 is connected at 258 to oneinput of a two-input AND gate 260 with inverting input logic, thusfunctioning as a NOR gate. The output of the gate 260 is the digitalheart sound signal 76. The second input 262 of the gate 260 is connectedto the Q output of the monostage 254. The output of the gate 260 is alsoconnected to the negative trigger input of the monostable stage 254.

The window trigger selector stage 92 includes a first two-input AND gate263 with inverting input logic with a first input being connected to anE gate signal. The second input of the gate 263 is connected to the Qoutput of the monostage 254. A second two-input AND gate 264 withinverting input logic includes a first input connected to a T gatesignal. The second input to the gate 264 is connected through a resistorto the ECG R-wave signal 96. The outputs of each of the gates 263 and264 are respectively connected to one input of a two input NOR gate 266.The output of the NOR gate 266 is the trigger select signal 94. The Tgate signal corresponds to the timed mode of operation and the E gatesignal corresponds to the ECG R-wave triggered mode of operation forheart sound detection. The T gate and E gate signals are provided bymeans of the switch 97 which functions in the E (ECG R-wave) mode toground the T gate signal and correspondingly in the T (time) mode toground the E gate signal.

The digitally variable time window stage 90 (FIG. 4h) includes a firstwindow stage. The first window stage includes a four stage analog switchdevice 268 and a monostable stage 270. The control signal from each ofthe respective four stages in the analog switch device 268 selectivelycontrols the connection of one resistor in the array 272 to the timinginput of a monostable stage 270. The trigger select signal 94 isconnected to a negative trigger input of the monostable stage 270. Thecontrol inputs of the stages of the analog switch device 268 arerespectively controlled by logic gates in a logic gate array 274 suchthat the respective W1 through W4 inputs of the selection signal 78control the device 268 in the T mode. In the E mode of operation, the Egate signal controls a predetermined fixed selection of the resistorarray 272.

The Q output of the monostable stage 270 in the first window stageprovides the heart sound enable signal 98(Q) and the Q output of themonostable stage 270 provides the heart sound enable signal 98(Q). Theenable signal 98(Q) is connected to the positive trigger input of amonostable stage 276 in a second time window stage of the digitallyvariable time window stage 90. The timing of the monostable stage 276 iscontrolled at a timing input by a four stage analog switch device 278.The selection of one or more resistors in a resistor array 279 iscontrolled by the data selection signal 78 including the W1 through W4control lines at the control input of the switch device 278.

In Q output of the monostage 276 provides the second heart sound andenable signal 104 utilized in the E mode of operation. In the T mode,the enable signal 98(Q) is utilized as a second heart sound enablesignal. In the E mode of operation, the heart sound enable signal 98(Q)is utilized as a first heart sound enable signal and the enable signal104 is utilized as a second heart sound enable signal by the window modecontrol stage 100.

The window mode control stage 100 (FIG. 4i) includes a first heart soundenable logic gate array 280 and a second heart sound enable logic gatearray 282. The first heart sound logic gate array 280 includes atwo-input AND gate 284 with inverting input logic operable in the T modeand a second two input AND gate 286 with inverting input logic operablein the E mode. One input of the T mode gate 284 is connected to theenable signal 98(Q) and the second input is connected to the E gatesignal. A first input of the gate 286 is connected to the enable signal98 (Q) and the second input is connected to the T gate signal. Theoutputs of the gates 284 and 286 are respectively connected to one inputof a two-input NOR gate 288 of the first heart sound enable array 280.

The second heart sound enable logic array 282 includes a firsttwo-input, T mode AND gate 290 with inverting input logic and a secondtwo-input, E mode AND gate 292 with inverting input logic. The firstinput of the T gate 290 is connected to the enable signal 98(Q) and thesecond input is connected to the E gate signal. A first input of thegate 292 is connected to the heart sound enable signal 104 and thesecond input is connected to the T gate signal. The outputs of the gates290 and 292 are respectively connected to one input of a two-input NORgate 294. The output of the gate 288 is connected to one input of athree-input AND gate 296 with inverting input logic. The second input tothe gate 296 is connected to the Q output of a false prevention,flip-flop stage 300. The third input of the gate 296 is connectedthrough a resistor to the output of an inverter gate 302. The input tothe inverter gate 302 is provided by the heart sound signal 76. Theoutput of the inverter gate 302 is also connected to the second input ofthe gate 298. The output of the gate 298 is connected through aninverter gate to provide the second heart sound trigger pulse signal108. The output of each of the gates 296 and 298 is respectivelyconnected through output driver stages to provide additional externaloutput trigger signals in addition to and independent of the triggerselect stage 110 that provides the selected, main system trigger outputat 112.

Considering now the operation of the heart sound detection andtriggering apparatus 10 in the T mode operation wherein first and secondheart sounds are detected based on the timing between the first andsecond heart sounds and referring now to FIG. 5, the T gate signal ishigh and the E gate signal is low with the selector switch 97 in the Tmode position. Upon the occurrence of a heart sound signal at 72 fromthe comparator 70 (FIGS. 1 and 4f), the monostable stage 256 (FIG. 4g)of the digital filter stage 74 is triggered.

Upon the triggering of the monostable stage 256, the heart sound pulsesignal at 76 provides a high level pulse signal that triggers themonostable stage 254 of the digital filter 74 on the falling edge of thepulse signal at 76. With the monostable stage 254 triggered, the Qoutput at 262 provides a high level lock-out window signal to inhibitadditional heart sound signals from 72 during the variably selectedlock-out window inhibit time via selection signal 78. As discussedhereinbefore, the lock-out inhibit time is the shortest systolicinterval for the file table value of operation presently beinginterrogated as selected from the digital integrator 80 and the displayand control file 84.

The monostable stage 254 at the Q output also enables the T gate 263 andthus the gate 266 to provide the trigger select enable signal 94 to thedigitally variable time window stage 90.

The trigger enable signal 94 triggers the monostable stage 270 (FIG. 4h)to provide at the 98Q and 98Q outputs the program timing window signalsto enable second heart sound detection with the timing window beingvariably determined by the selection signal 78. The enable signal 98(Q)disables further first heart sound detection via gates 284, 288 and 296(FIG. 4i). The enable signal 98(Q) through gates 290, 294 and 298provides a second heart sound enable signal.

During the window time in which the gate 294 provides an enable signalthrough the gate 298, if a second heart sound signal at 76 is received,the output of the gate 298 through the inverter gate will provide asecond heart sound pulse trigger signal at 108 as shown in FIG. 5 at304. As discussed above, if no second heart sound occurs during thevariable window time for detecting a second heart sound the 98Q signalchanging state at 306 in FIG. 5, no second heart sound will be detected.

The time of enablement for detection of the second heart sound after theoccurrence of the first heart sound is set to the longest diastolicinterval for the table file value being interrogated as determined bythe display and control file 84 in accordance with the timing input 86from the system timing control 88.

Considering now the E mode of operation of the heart sound detection andtriggering apparatus 10 and referring to FIG. 6, with the triggerselection switch 97 in the E mode position, the T gate signal is low andthe E gate signal is high. Upon the occurrence of the ECG R-wave signalat 96 at the gate 264 (FIG. 4g), a trigger select signal 308 (FIG. 6) at94 is provided through the gates 264 and 266. The pulse signal 308 at 94triggers the monostable stage 270 (FIG. 4h) to provide a time enablewindow 310 (FIG. 6) at the 98(Q) output for a fixed time interval set inthe E mode by the E gate signal through the logic gate array 274, theswitch device 268 and the resistor array 272. It should be understoodthat in discussing the various monostable stages, a respective timingcapacitor of fixed value is also utilized in additon to the resistorarrays 252, 272 and 279 (FIGS. 4g and 4h) to provide the various timeconstants.

The 98Q signal along with the T gate signal enables the gate 286 andthus the gate 288 (FIG. 4i). Accordingly the gate 296 will provide afirst heart sound signal at 106 (FIG. 6) upon the occurrence of a heartsound signal at 76. As before when a heart sound signal at 72 from thecomparator 70 triggers the monostable stage (FIG. 4g), a heart soundsignal at 76 is provided.

Further, upon the occurrence of a signal at 76, the monostable stage 254(FIG. 4g) of the digital filter stage 74 is triggered to provide alock-out inhibit window time as variably set by the selection data 78 toinhibit further heart sound signals at 72 if they occur during theinhibit window time. The inhibit window time is set to the shortestdiastolic time for the table value being interrogated by the apparatus10.

After the time-out of the enable window provided by the monostable stage270 (FIG. 4h) for the first heart sound enable, the 98(Q) signaltriggers the monostable stage 276. Thus the monostable stage 276 at theQ output provides a second heart sound enable signal 104 for thevariably set time window 312 (FIG. 6) to enable gates 292 and 294.Further the gates 284 and 288 are now disenabled by the time-out of thewindow signal at 98(Q) and thus the first heart sound enable logic gatearray 280 is disabled from producing further heart sound pulses.

During the enable time window 312, if an additional heart sound pulseoccurs after the window inhibit time provided by the monostable stage270, (FIG. 4h) the gate 298 (FIG. 4i) is enabled to provide a secondheart sound signal 108 (FIG. 6).

Considering now operation of the display and control file 84 inaccordance with the system timing control stage 88 and the digitalintegrator and timing control stage 80, the following Table A depicts anillustrative example of one specific embodiment of the apparatus 10 forappropriate heart detection. Table A describes the ranges of operationto accurately detect the heart sounds and to avoid missing or falselydetecting heart sounds; e.g. a first occurring heart sound as systolicand a second occurring heart sound as a diastolic which would result inan erroneous determination. The first column entitled W1-W4 DigitalInput at 78 includes the range of 0 through 15 and represents the binarydata on the selection input 78 as output from the digital integrator andtiming control stage 80 to program the timing windows of the monostablestages 254 and 276 in the E mode of operation and the timing windows ofstages 254, (FIG. 4g) 270 and 276 in the T mode of operation.

The second column of Table A entitled "Window Times at 270, 276 [of thedigitally variable time window stage] 90" depicts in milliseconds thewindow times set at monostables 270 and 276 in the time mode and thewindow set in monostable stage 276 in the E mode. The second throughseventh columns represent the values in milliseconds. The second columnrepresents the various time windows corresponding to the digitalselection data in the first column. The fifth column entitled "WindowTime [monostable stage] 254 of [digital filter stage] 74" depicts thevariable window time settings corresponding to the W1 through W4 digitalinputs at 78.

                                      TABLE A                                     __________________________________________________________________________    W1-W4   WINDOW TIMES                                                                            HEART                                                                              HEART            HEART    ADDRESS  DATA                DIGITAL IN-                                                                           AT 270, 276                                                                             PERIOD                                                                             PERIOD  WINDOW TIME                                                                            PERIOD   86       AT 82               PUT AT 78                                                                             OF 90 (A) A/.333                                                                             (A + 70)/.666                                                                         254 OF 74 (B)                                                                          (B + 20)/.333                                                                          TO 84    TO                  __________________________________________________________________________                                                              80                  0       NO OPERATION                            →                                                                        4096                        1       1329      3987 2098    587      1821             →                                                                        1                                                                  →                                                                        2519                        2       980       2940 1575    433      1359             →                                                                        2                                                                  →                                                                        1626                        3       559       1677 943     248      804              →                                                                        3                                                                  →                                                                        1233                        4       508       1524 867     226      738              →                                                                        4                                                                  →                                                                        981                         5       365       1095 652     162      546              →                                                                        5                                                                  →                                                                        824                         6       332       996  603     147      501              →                                                                        6                                                                  →                                                                        696                         7       263       789  499     117      411              →                                                                        7                                                                  →                                                                        612                         8       242       726  468     108      348              →                                                                        8                                                                  →                                                                        538                         9       203       609  409     91       333              →                                                                        9                                                                  →                                                                        492                         10      192       576  393     86       318              →                                                                        10                                                                 →                                                                        447                         11      167       501  355     76       285              →                                                                        11                                                                 →                                                                        420                         12      162       486  348     72       276              →                                                                        12                                                                 →                                                                        390                         13      144       432  321     64       252              →                                                                        13                                                                 →                                                                        367                         14      138       414  312     62       246              →                                                                        14                                                                 →                                                                        342                         15      124       372  291     56       228       ↓                                                                             →                                                                        15                 __________________________________________________________________________

In the specific example represented in Table A for various ranges ofoperation in accordance with file table values in the display andcontrol file 84, the third and fourth columns labeled respectively"Heart Period A/0.333" and "Heart Period (A+70)/0.666" represent theextremes of allowable operations for each corresponding window time ofoperation in column two and the digital selection value in column one.

For example, considering the table entry corresponding to the W1 throughW4 input 7, with a window time of 263 milliseconds for the monostablestages 270 and 276 in the T mode operation, the value 789 millisecondsderived by A/0.333 corresponds to the period of the lowest heart ratefor which the window enable time of 263 milliseconds will providedetection of the systolic heart sound if the first heart sound thatoccurs is diastolic. The fourth column entry 499 milliseconds derivedfrom (A+70)/0.666 corresponds to the heart period for the maximum heartrate for accurate operation within the setting of W1 through W4 at 7with the longest permissible window equal to 263 milliseconds to avoidimproper detection from a first occurring systolic signal and a secondoccurring diastolic heart sound signal. The column 6 entry 411milliseconds derived from (B+20)/0.333 with an inhibit window of thedigital filter 74 of 117 milliseconds corresponds to the period of themaximum heart rate that can be detected based on the shortest systolicheart pulse after the occurrence of a diastolic heart pulse. For thevalues in Table A, a ratio of systolic interval equal to one-third ofthe overall heart cycle and a ratio of diastolic interval equal totwo-thirds of the heart cycle are utilized. Of course it should beunderstood that various other specific ratios could be utilized ifdesired.

With these parameters established for a specific embodiment, the seventhcolumn corresponds to the data signal at 86 from the system timingcontrol 88 at which the display and control file 84 will be controlledto output at 82 the appropriate address for the range of operation tothe digital integrator stage 80.

Referring now to FIG. 7, the appropriate window enable times for thevarious monostables 270, 276 and 254 (FIGS. 4g and 4h) are graphicallydepicted along with the selected window times of operation in thespecific embodiment for a selected corresponding range of heart cycleperiod for appropriate operation. For example, the area between theupper inclined line 320 and the lower inclined line 322 representpermissible enabled window times for the monostable stage 270 in the Tmode and the monostable stage 276 in the E mode relative to thecorresponding heart cycle periods along the horizontal axis. The actuallines from the E mode are slghtly offset due to the ECG-R signal 96(FIG. 6) time of generation. The upper steps or staircase depiction 324represents the window enable times for the monostable stage 276 in the Emode and the monostable 270 in the T mode for the specificimplementation to practice the present invention in accordance withTable A. The lower steps or staircase depiction 326 graphicallyillustrates the window enable times for the ranges of operation in TableA in a specific implementation for the monostable stage 254 (FIG. 4 g)of the digital filter 74. The window times corresponding to the digitalinput at 78 with values 1 through 7 are indicated in a relativelyaccurate manner while the remaining 8 through 15 window enables rangesare only approximately indicated due to the accuracy of the graphicscale.

In accordance with FIG. 7, the line 320 represents the relationshipbetween maximum period of heart rate that can be appropriately detectedfor the corresponding window time while the lower line 322 representsthe minimum heart cycle period at which the corresponding intersectingwindow enable time will accurately distinguish between first and secondheart pulses without false indications. Thus, the lower line 322corresponds at each entry to the enable window time approximately equalto the diastolic interval for the heart cycle period.

Referring now again to FIG. 4j and considering the display and controlfile stage 84, two INTEL type 2732 ROM stages 330 and 332 are providedin the specific implementation that are addressed by the system time andcontrol data signals 86. In response, the ROM stages 330 and 332 outputrespective portions of the rate display data signals 132 to the timinginterval or rate convert select stage 126 and the data range signals 82to the digital integrator stage 80. Referring now to the eighth columnof Table A entitled Data at 82 to 80, the data on the lines 82 as listedin Table A corresponds to the address ranges at 86 from column 7 ofTable A; i.e. the data at column 8 is output corresponding to the upperand lower ranges of the address data 86. For example, if the address 86from the system timing control stage 88 outputs a count equal to a valuebetween 824 and 981, the display and control file stage 84 at output 82provides binary data equal to 5.

The digital integrator stage 80 (FIG. 4i) is implemented by a four stageadder device 334, a four stage flip-flop device 336, J-K flip-flop stage338, an inverter gate 340, and a two input AND gate 342. The digitalintegrator 80 is arranged to output the data signals at W1 through W4 at78 from the respective Q outputs of the four stage, flip-flop device336. The range data signals 82 from the display and control file 84(FIG. 4j) are connected to the A input of each stage of the four stageadder device 334. Further the Q outputs of each stage of the flip-flopdevice 336 are respectively interconnected to the B inputs of the fourstage adder device 334. The sum outputs of the second, third and fourthadder stages of device 334 are respectively connected to the D input ofthe first, second and third flip-flop stages of device 336. The carryoutput of the fourth adder stage is connected to the D input of thefourth flip-flop stage of device 336. The sum output of the first adderstage is connected to the J input and is also connected through aninverter gate 340 to the K input of the flip-flop 338. The clock of theflip-flop 338 is connected to the output of the gate 342. The inputs tothe gate 342 are a latch signal and a binary signal.

In operation, the digital integrator stage 80 is arranged to provide atdata output 78 on lines W1 through W4 a value equal to one-half of thesum of the previous output at 78 plus the data input at 82. The summingoperation is performed upon each clock to the device 336 provided by thelatch and binary signals through the AND gate 342.

The system timing control stage 88 (FIG. 4c) includes four counterstages 344, 346, 348 and 350 that are arranged in cascade to provide thecount data output 86 with respective data outputs 1A through 1D fromcounter 344, 2A through 2D from counter 346, 3A through 3D from counter348, and 4A through 4D from counter 350. The input to the cascadedcounter stages 344, 346, 348 and 350 is connected at the clock input ofcounter 344 from the output 352 of the system timing clock oscillatorstage 136 (FIG. 4b). The system timing clock stage 136 is enabled by theenable signal 138 from the logic devices of the display input selectionand pulse-to-pulse gate stage 122.

The system timing control stage 88 also includes an overflow inhibitarrangement 354 (FIG. 4c) provided by an array of logic gates to providea full scale stop signal at 356. The full scale stop signal 356 isconnected in the display input selection stage 122 to disable operationof the system timing clock 136 (FIG. 4b) via the enable signal 138.

Consider now the operation of the apparatus 10 (FIG. 1) as illustratedby a typical example of heart sound detection with the selection switch123 including switch poles 123a, 123b and (FIG. 4a) of the display inputselection stage 122 being set to the one position for first to secondheart sound operation and with the trigger selection switch 97 (FIG. 4g)in the T mode. Operation of the apparatus 10 commences with the dataselection 78 providing an output representing the digital number 15 soas to set the window time of the monostable stage 270 (FIG. 4h) to 124milliseconds and the window inhibit time of the monostable stage 254(FIG. 4g) to 256 milliseconds. The operation of the apparatus 10commences as described hereinbefore assuming maximum heart rates toinsure proper detection being established by a procedure as follows.

Assuming that the heart rate of the patient being monitored is notwithin the range 15 in Table A corresponding to the heart period beinggreater than 372 milliseconds, the display input selection stage 122(FIG. 1) will enable accumulated counting in accordance with the clockinput of the system timing stage 88 upon the occurrence of the firstheart sound signal 106 remembering that this first heart sound pulse at106 may be either diastole or systole as will be determined.

If the heart rate is slower than a period corresponding to 372milliseconds, no second heart sound at 108 will be detected by theapparatus 10 and the counters 344, 346, 348 and 350 (FIG. 4c) willaccumulate counts to cause a full scale stop to be generated at 356wherein the binary signal at 360 will be generated and the output to thedisplay and control file 84 (FIG. 4j) at 86 will be a full scale 4,096count. In response, the display and control file 84 for the nextdetection cycle will output a binary 1 representation to the digitalintegrator stage 80 (FIG. 4i) via data lines 82. In response the digitalintegrator stage 80 at 78 will output a binary value 8 to condition thewindow time of monostable stage 270 (FIG. 4h) to a 242 millisecond valueand a window inhibit time of 108 milliseconds for the monostable stage254 (FIG. 4g). In this next cycle of operation, the system timingcontrol 88 (FIG. 4c) again begins counting upon the occurrence of afirst occurring heart sound and if the heart rate is slower than aperiod equal to 726 milliseconds, the second heart sound will not bedetected and the display and control file stage 84 (FIG. 4j) will becontrolled to again output a one binary value at 82 to the digitalintegrator stage 80 (FIG. 4i). In response, the digital integrator stage80 will output a four binary value at 78 and condition the monostablestage 270 (FIG. 4h) to provide a window enable time of 508 millisecondsand a window inhibit time for monostable 254 (FIG. 4g) of 226milliseconds. Thus, operation continues throughout the ranges ofoperation of Table A until heart sound detection is achieved. For fasterheart rates, a fewer number of detection cycles are required in order toachieve synchronization for proper detection.

Once proper heart sound detection is achieved in one of the variousranges of operation, a first heart sound being diastole will start thecounting in the system timing stage 88 (FIG. 4c) and the second heartsound signal at 108 (FIG. 4a) will stop the counting. Thus in each suchcycle, the data value at 86 represents the time interval from the firstto second heart sounds as provided to the timing interval or rateconvert select stage 126 (FIG. 4j). Further the display input selectionstage 122 (FIGS. 4a,4b) will be in a decimal mode of operation and theselect line 124 (FIG. 1) will condition the time interval rate selectorstage 126 to provide the time interval data 86 to the display 130 viathe selector output 128 (FIG. 4j). Thus the correct first to secondheart sound time interval will be displayed as a read out by the display130 for each cycle of detection. The display 130 is also provided with aheart beat indicator to indicate by a short on-time the heart rate ofthe patient for clarification purposes. The apparatus 10 includes aheart beat stage 357 (FIG. 4i) to provide the heart beat signal to drivethe display indicator. Further, the operator by means of a CRT displayand the heart sound trigger signals at 359 and 361 (FIG. 4i) can viewthe actual heart sound signal timing to confirm the proper detection isbeing achieved.

After proper heart detection is established within the range ofoperations spanning typical heart rates from 15 to 250 beats per minute(heart cycles per minute), the display will provide the first to secondheart time interval and the time interval at 86 will appropriatelyaddress the display and control file 84 to control the range ofoperation of the apparatus 10 through the digital integrator stage 80.For example, if synchronized heart detection is achieved in range 8 ofoperation of the Table A, and the next succeeding detection cycleresults in a time interval at 86 equal to 450 milliseconds, the displayand control file 84 will output a data value 10 to the digitalintegrator stage 80 and the selection data at 78 will control operationin range 9 (see FIGS. 1,4i and 4j).

Concerning other display input selection modes, the switch levels 123a,b and c (FIG. 4a) appropriately connect the corresponding trigger signalinputs to provide the first and second trigger signals to the inputselection stage 122 in each of the eight positions to provide anappropriate determination of the rate or time interval functionselected.

A heart sound threshold setting arrangement 360 is provided in the heartsound comparator stage 70. In the specific embodiment of FIG. 4, a hi orlow threshold setting switch 362 is provided. Thus, the level of theheart sound signal at 86 to produce the digital heart sound signal at 72can be selected by the threshold setting arrangement 360. In otherspecific embodiments, the comparator 70 is arranged to produce the heartsound signal at 72 at predetermined portions of the heart sound signalat 68. For example, in one specific embodiment, the comparator 70 isarranged to provide the signal at 72 on the upward, rising slope of thesignal at 68. In another specific embodiment, the comparator is arrangedto provide the signal at 72 on the downward, falling slope of the signalat 68.

Further, while the generation of the heart sound trigger pulse signalsat 106 and 108 of FIG. 4 (FIG. 4j) have been described as occurringcoincident with the heart sound signal pulse at 76, (FIG. 4g) it shouldbe realized that in other specific embodiments the stages 74, 92, and100 (FIGS. 4g,4j) are arranged to generate the trigger pulse signals at106 and 108 in accordance with other predetermined time relationshipswith respect to the heart sound signals at 72, 258 and 76 (FIG. 4g) toachieve the desired time of generation of the heart sound trigger pulsesignals at 106 and 108.

Considering now one arrangement for the control of diagnostic apparatusin accordance with the present invention and referring now to FIG. 8,cardiac data at 400 from cardiac analysis apparatus (not shown) isconnected to the data input of a temporary storage (scratch-pad) memory402. The data at 400 represents particular cardiac analysis data forevaluating cardiac performance; e.g. blood pool studies or blood poolvolume data from radiation detection apparatus such as a scintillationcamera.

The temporary storage memory 402 receives data at 400 as a function oftime and stores the accumulated data in selected time interval frames.The selected time intervals are sufficiently short to ensure appropriateanalysis at a desirable number of points. For example, in blood poolstudies including ejection fraction determination and volume curves itis essential to acquire data representing appropriate stop-action imagedata of the heart and to analyze the data at the appropriate times interms of heart function operation. Thus, the data acquisition frames ortime intervals must be short enough to satisfy all desirable analysiscriteria. For example, data frames of 10 milliseconds or less arerequired in specific analysis arrangements in connection with rapidheart rates.

In order to appropriately select the stored image data for analysis, aportion controller 404 is provided that outputs an address controlsignal at 406 to select the portion of the data frames in the temporarystorage memory 402 that is determined to be required for appropiate andaccurate data analysis of the cardiac functions being analyzed.

The portion controller 404 in a specific embodiment receives as inputsthe second heart sound signal trigger 108 and a system trigger signal112 from the heart sound detection and triggering apparatus 10 todetermine the appropriate data frames.

In a preferred embodiment, the temporary storage memory 402 is alsocontrolled by a data control signal 408 provided as an output from anarrhythmia detector 410. When the arrhythmia detector 410 determinesthat the data in the temporary storage memory 402 corresponds to a heartcycle that represents invalid or confusing data, the data control signal408 functions to cause the temporary storage memory to erase the data.

The arrhythmia detector 410 includes the system trigger signal 112 as aninput for determining whether or not a present heart cycle represents anarrhythmia cycle and should be disregarded for data analysis purposes.In specific embodiments, the arrhythmia detector 410 interrogates thefirst heart sound to first heart sound timing interval or the ECG R-waveto ECG R-wave time interval as selected by the system trigger signal 112for a predetermined number of previous heart detection cycles andcompares the average of the previous cycles with the parameter of thepresent cycle. If the present cycle represents a departure of more than±25% from the previous average, the data control signal at 408 functionsto discard the data in the temporary storage memory 402. In one specificembodiment, four previous heart cycles are averaged.

The temporary storage memory 402 is controlled to accept data in adefined heart cycle in accordance with the input trigger signal at 112.Thus the temporary storage memory 402 accepts data in predetermined dataframes for each heart cycle with start and stop data acquisition signalsin coincidence with the system trigger signals at 112.

The selected data from the temporary storage memory 402 is output at 412to a data framing stage 414. After appropriate framing of the data from412, the data framing stage 414 outputs the appropriately framed data at416 to an actual analysis memory 418 of diagnostic apparatus. The dataframing stage 414 receives a frame control signal at 420 from theportion controller 404.

Specific diagnostic apparatus including the actual memory 418 that issuitable for the analysis in accordance with the present invention isthe SCINTIVIEW™ data analysis apparatus available from SiemensGammasonics, Nuclear Medicine Division.

In operation, the temporary storage memory 402 is controlled by thesystem trigger signal 112 to acquire data at 400 for each heart cycleafter the collection of the data. Assume that the arrhythmia detector410 determines that the heart cycle is valid for analysis based on thesystem trigger signals at 112. In accordance with the second heart soundsignal at 108 occurring during the heart cycle for which data isobtained, the portion controller 404 determines the data frames withinthe temporary storage memory 402 that are of interest for analysis.Thus, the portion controller outputs at 406, the address signals thatrepresent the data frames to be output to the data framing stage 414.Further, after the output of data at 412, the temporary storage memoryerases the stored data. In this regard the data from two or more heartcycles may be simultaneously stored within the temporary storage memory402. The portion controller 404 also outputs the control framing signal420 to condition the data framing stage 414 to appropriately format theoutput at 412 into a desired number of data frames suitable for use bythe diagnostic apparatus. For example, in a specific embodiment, thedata framing stage 414 appropriately frames the selected data at 412into 16 data frames.

Thus, the arrangement of FIG. 8 functions to control the acquisition ofdata and perform a mid-course cardiac cycle correction for selectingappropriate data for analysis for imaging purposes. Specifically, assumethat the temporary storage means 402 is arranged to store data in 10millisecond frames with a total number of 100 data frames for aparticular heart detection cycle. Further, assume that the portioncontroller 404 receives the second heart signal at 108 coincident withthe 33rd data frame time interval. In accordance with the controlsettings of the portion controller 404, the signal 406 directs thetemporary storage memory 402 to read out the 33rd through 67th dataframes at 412 while the remaining data is either erased immediately ormerely disregarded. The control signal 420 provides a framing intervalsignal such as to define 16 data frames of approximately 20 milliseconddata frame intervals. Of course, it should be understood that adifferent range of data frames such as the 25th to 60th frames or anyother range may be selected for analysis relative to the systole triggersignal 108 with any desired data frame interval in accordance with theanalysis purpose.

It should be understood that the arrhythmia detector 410 and the portioncontroller 404 in specific embodiments are capable of independentoperation relative to each other in the control of the temporary storagememory 402.

Considering other specific arrangements for the control of diagnosticapparatus by the present invention, the second heart sound signal eitherat 108 or as selected by the system trigger selector 110 at 112 (FIG.4a) is utilized to directly control the acquisition of data bydiagnostic apparatus to accurately acquire data for analysis for gatedblood pool studies or the like.

Prior detection and gating techniques utilizing the ECG R-wave delaytriggering are extremely susceptible to problems during stress teststudies. As the heart cycle changes rapidly, the programmed delay willno longer approximately gate the analysis data at systole. Some priorsystems have attempted to ignore heart cycle data by averagingtechniques such as by rejecting all heart cycle data when the R-R wavesignal rate varies by more than a predetermined amount. Sucharrangements are unable to properly evaluate and accept data due to therapidly changing heart rate. In the case where arrhythmia is present,effective data analysis and triggering becomes extremely complex andnearly impossible.

This mode of operation utilizing an accurately timed systolic heartsound is especially useful in analyzing the cardiac function of patientsundergoing stress studies wherein noise on the heart sound signal inputis at increased levels rendering prior known heart sound detection andgating techniques extremely inaccurate and unreliable. Thus, accuratesystolic gating or analysis utilizing the systolic heart sound triggeras a reference point is extremely valuable to achieve meaningfulanalytical results.

The control of diagnostic apparatus with the use of the presentinvention is also extremely useful for analysis by gating an image ordata analysis with the diastolic (first heart sound trigger signal) andby gating an image or data analysis with the systolic (second) heartsound trigger signal for an accurate and simple assessment of leftventricular ejection fraction and heart wall motion. Further, thesystole (second) heart sound trigger signal can be utilized to triggermultiple gated images to start a study at the systole point of thecardiac cycle and to evaluate the rate and quality of left ventricularfilling phase.

While there has been illustrated and described various embodiments ofthe present invention, it will be apparent that various changes andmodifictions thereof will occur to those skilled in the art. Forexample, the display and control file stage 84 and the digitalintegrator stage 80 in an alternate embodiment are arranged to operatestep by step in a predetermined manner throughout the fifteen ranges ofoperation. For example, the display control file 84 in another alternateembodiment is arranged to step through the 15 values of operationstarting from value 15 one step at a time to range one until properdetection is achieved. Further the display and control file stage 84 incombination with other stages of the apparatus 10 in another alternateembodiment are configured by a microprocessor to supply a continuouslyvariable time window control signal to the digital filter 74 and thedigitally variable time window stage 90 in accordance with the depictionof FIG. 7. Further, the ranges of operation are merely illustrative andcan of course be chosen as desired.

Accordingly, it is intended in the appended claims to cover all suchchanges and modifications as fall within the true spirit and scope ofthe present invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. Apparatus for detecting heart sounds and forgenerating accurately timed heart sound reference signals, the apparatusincluding first and second heart sound inputs, the apparatuscomprising:(a) means responsive to representations of heart sound signalinputs for generating at least one heart sound output signal coincidentwith systole at a first signal output in accordance with the timingrelationship between said received heart sound signal inputs; (b) meansfor establishing a heart sound enable time window in response to a firstreceived heart sound signal input; (c) means responsive to said heartsound enable time window and said heart sound signal inputs forgenerating said systole heart sound output signal in response to areceived heart sound signal input occurring during said heart soundenable time window; (d) window setting means for variably programmingpredetermined heart sound enable time windows in said heart sound enabletime window establishing means in accordance with predetermined detectedtiming relationship between received heart sound signal inputs, whereinsaid window setting means comprises means responsive to said heart soundsignal inputs determining a predetermined timing relationship andgenerating a data output, and means responsive to said data output foroutputting window setting control signals to said heart sound enabletime window establishing means; and (e) input selection means forselectively providing first and second trigger signals as respectivestart and stop signals to said timing relationship and data outputgenerating means, said timing relationship and data output generatingmeans providing said detected timing relationship in response to saidfirst and second trigger signals as a representation of the timeinterval between said respective start and stop signals;wherein saidinput selection means includes an ECG R-wave signal input among aplurality of predetermined, signal inputs said heart sound outputgenerating means further comprising means for generating at a secondsignal output a heart sound output signal coincident with diastole, saidfirst and second heart sound signal outputs being provided as inputs tosaid selection means.
 2. The apparatus of claim 1 wherein said inputselection means includes switch means for selectively providing in arespective one of said predetermined selection states as said first andsecond trigger signals, said first and second heart sound outputsignals, said first heart sound output signal, said ECG R-wave signal,said ECG R-wave signal and said first heart sound signal output, saidECG R-wave signal, and said second heart sound signal outputs.
 3. Theapparatus of claim 2 wherein said switch means further comprises rateselection states corresponding to first heart sound signal output tofirst heart sound signal output rate, and ECG R-wave signal to ECGR-wave signal rate.
 4. The apparatus of claim 3 further comprising rateconverter means responsive to said data output with said switch means insaid rate selection states for outputting rate display data to saiddisplay means corresponding to the rate represented by said data output.5. The apparatus of claim 4 wherein said rate converter means and saiddata store means comprise a single storage means including said dataoutput as an address.
 6. Apparatus for detecting heart sounds and forgenerating accurately timed heart sound reference signals, the apparatusof the type which includes heart sound inputs, the apparatuscomprising:(a) means responsive to representations of heart sound signalinputs for generating at least one heart sound output signal coincidentwith systole at a first signal output in accordance with the timingrelationship between said received heart sound signal inputs; (b) meansfor establishing a heart sound enable time window in response to a firstreceived heart sound signal input; (c) means responsive to said heartsound enable time window and said heart sound signal inputs forgenerating said systole heart sound output signal in response to areceived heart sound signal input occurring during said heart soundenable time window; (d) window setting means for variably programmingpredetermined heart sound enable time windows in said heart sound enabletime window establishing means in accordance with predetermined detectedtiming relationship between received heart sound signal inputs; (e) anECG R-wave signal input; and (f) trigger mode selection means forcontrolling detection operations of said heart sound output generatingmeans in a timed mode or an ECG R-mode;said time window establishingmeans further comprising ECG-R mode means responsive to said triggermode selection means for establishing a first heart sound enable timewindow after the occurrence of said ECG-R wave signal input, said secondheart sound enable time window establishing means being responsive tosaid ECG-R mode means to establish said second heart sound enable timewindow after said first heart sound enable time window.
 7. The apparatusof claim 6 wherein said time window establishing means comprises firsttime window generating means and second time window generating means,said first time window generating means being responsive to said timedmode of said trigger mode selection means to provide a second heartsound enable time window after the occurrence of a first received heartsound signal, said first time window generating means being responsiveto said ECG-R mode of said trigger mode selection means to provide afirst heart sound enable time window after the occurrence of said ECG-Rwave signal, said second time window generating means being responsiveto said ECG-R mode of said trigger mode selection means and said firsttime window generating means to provide a second heart sound enable timewindow.
 8. The apparatus of claim 7 wherein said heart sound outputsignal generating means is responsive to said first heart sound enabletime window in said ECG-R mode and a first received heart sound toprovide a diastole heart sound output signal, said heart sound outputsignal generating means being responsive to said second heart soundenable time window to provide a systole heart sound output signal when asecond received heart sound signal occurs within said second heart soundenable time window, said heart sound output signal generating meansbeing responsive to said second heart sound enable time window from saidfirst time window generating means in said timed mode to provide asystole heart sound output signal when a second received heart soundsignal occurs within said second heart sound enable time window.
 9. Theapparatus of claim 7 wherein said window setting means in said ECG-Rmode sets variable predetermined time enable windows in said second timewindow generating means and a fixed predetermined time enable window insaid first time window generating means, said window setting meanssetting variable predetermined windows in said first time windowgenerating means in said timed mode.
 10. The apparatus of claim 6further comprising ECG-R delay means responsive to said ECG-R wavesignal input for providing a selectively timed delay ECG-R delay signalthat is delayed from said ECG-R wave signal in accordance with theselective setting of a time delay input control to said ECG-R delaymeans.
 11. The apparatus of claim 10 wherein said heart sound outputgenerating means further comprises means for generating a heart soundoutput signal coincident with diastole at a second signal output. 12.The apparatus of claim 10 further comprising output signal selectionmeans having as inputs said first and second signal outputs, said ECG-Rwave signal and said ECG-R delay signal for selectively providing one ofsaid inputs at a system trigger output.